From an evolutionary standpoint, humans should become more aggressive when they see meat. But research indicates the exact opposite is true.

In theory, humans can have innate predispositions to certain stimuli. These reactions would be vestiges of natural selection, in that early humans who had the most successful gut reaction would gain an evolutionary advantage. One obvious example might be a fear of large predators like lions. Humans whose first instinct was to quietly get away from the lions were more likely to live and pass on their genes than those who went right up to the lions to investigate.

Of course, it's tricky knowing where an innate reaction ends and a learned behavior begins. One way to key in on more instinctual reactions is to design experiments that don't directly deal with responding to the stimuli. In this case, researchers at McGill University asked 82 males to listen to a script reader while they sorted photos. Some of the photos were images of meat, while others had neutral images that were unlikely to provoke any particular reaction in the participants.

Whenever the reader made an error, they were asked to punish him, it and it was up to the test subjects to decide on the severity of the punishment. (For anyone worried about the poor script reader, these punishments were purely hypothetical.) The scientists expected the meat photos to cause more aggressive reactions to the script reader's errors on the part of the test subjects, as chief researcher Frank Kachanoff explains:

"I was inspired by research on priming and aggression, that has shown that just looking at an object which is learned to be associated with aggression, such as a gun, can make someone more likely to behave aggressively. I wanted to know if we might respond aggressively to certain stimuli in our environment not because of learned associations, but because of an innate predisposition. I wanted to know if just looking at the meat would suffice to provoke an aggressive behavior."

But that isn't what happened at all. Instead, the pictures of meat actually made the subjects less aggressive. That certainly suggests the subjects did have some kind of innate reaction to the meat, but not the one the researchers expected. After all, ancient humans would have associated meat with hunting and the competition for and protection of food resources. Those are all tasks where aggression would be a definite advantage, but these results suggest the exact opposite.

Kachanoff is pretty sure he knows why the experiment produced those results. He simply showed his subjects the wrong sort of meat:

"We used imagery of meat that was ready to eat. In terms of behaviour, with the benefit of hindsight, it would make sense that our ancestors would be calm, as they would be surrounded by friends and family at meal time. I would like to run this experiment again, using hunting images. Perhaps Thanksgiving next year will be a great opportunity for a do-over!"